AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Circuit symbols, charge and current
Electricity · Lesson 1 of 10
Warm-up
Answer each one, then check.
1. What is the unit of current?
The ampere (A)
2. What is the unit of time in physics calculations?
The second (s)
3. Which particles carry current in a metal wire?
Electrons
4. What does a battery provide?
A potential difference (a push for charge)
5. Convert 2 minutes to seconds.
120 s
Learning Objectives
1. Draw and interpret circuit diagrams using standard symbols.
2. State that a source of potential difference is needed to make charge flow in a closed circuit.
3. Recall and apply Q = It.
4. State that the current has the same value at any point in a single closed loop.
Charge And Current
charge flow = current × time Q = It
Electric current is a flow of electrical charge. The size of the current is the rate of flow of charge. Charge is in coulombs (C), current in amperes (A) and time in seconds (s).
Standard Circuit Symbols
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Learn to draw these quickly and neatly. |
The standard circuit symbols for a cell, battery, switch, lamp, resistor, variable resistor, fuse, ammeter, voltmeter, diode, LDR and thermistor.
Drawing a Circuit Diagram
Use a ruler and standard symbols.
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1 Start with the power supply Draw a cell or battery. |
2 Add components in series Draw straight lines with square corners; no gaps. |
3 Add the ammeter in series It goes in the main loop where you want to measure current. |
4 Add the voltmeter in parallel It goes across the component you are measuring. |
5 Check Every component is joined by lines and the loop is closed. |
Charge Flow
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A current of 3.0 A flows through a lamp for 20 s. Calculate the charge that flows. |
1. Write the equation
Q = It
2. Substitute
Q = 3.0 × 20
3. Answer
Q = 60 C
Answer: 60 coulombs
Finding the Current
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240 C of charge flows through a heater in 2 minutes. Calculate the current. |
1. Convert the time
2 min = 120 s
2. Rearrange
I = Q ÷ t
3. Substitute
I = 240 ÷ 120
4. Answer
I = 2.0 A
Answer: 2.0 A
Key Ideas
Learn these.
▸ A source of pd is needed. For charge to flow round a closed circuit there must be a source of potential difference, such as a cell.
▸ Current in a series loop. The current has the same value at every point in a single closed loop.
▸ Current is not used up. Charge keeps flowing round the loop; the components transfer energy from the charge.
▸ Ammeter and voltmeter. Ammeter in series measures current. Voltmeter in parallel measures pd.
Key Terms
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Electric current The rate of flow of electrical charge. |
Charge A property of matter that can be positive or negative; measured in coulombs. |
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Ampere The unit of current; one coulomb per second. |
Coulomb The unit of charge. |
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Ammeter Measures current; connected in series. |
Potential difference The energy transferred per unit of charge; measured in volts. |
Your Task: Circuit Doodles
12 minutes
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Draw circuit diagrams for: (a) a cell, a switch and a lamp in series; (b) the same circuit with an ammeter to measure the current in the lamp and a voltmeter to measure the pd across it. 1. Draw the loop with a ruler. 2. Add the meters in the right way. |
A good answer shows: (a) A loop containing a cell, closed switch and lamp. (b) The ammeter is in the loop (series); the voltmeter is drawn in parallel with the lamp only.
Can I...?
☐ Recognise standard circuit symbols.
☐ Draw a series circuit.
☐ Place an ammeter and voltmeter correctly.
☐ Use Q = It.
☐ Rearrange for current or time.
☐ Convert minutes to seconds.
☐ Explain why current is the same round a series loop.
☐ State what is needed for charge to flow.
Summary
✓ Q = It.
✓ Symbols: cell, lamp, ammeter (A), voltmeter (V), and so on.
✓ Ammeters in series, voltmeters in parallel.
✓ Current is the same at every point in a series loop.
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EXAM FOCUS A current of 0.40 A flows for 30 s. Calculate the charge that flows. (2 marks) Write the equation, substitute, and include the unit C. |